Wind turbine gearboxes need to have a certain gap between its components for several purposes such as avoid interference, wear, and excessive heat generation, ensure proper lubrication or compensate for manufacturing tolerances. Said gaps cause that at a load reversal the output shaft will turn a slight angle even though the input shaft is not rotating. The value of the shaft “turn angle at zero load” is called the rotational backlash of the gearbox.
If the main shaft torque in the gearbox is zero, then the forces acting in the gear mesh will be approximately zero. Then there will be no tension of the drive train and some backlash will be present.
If the main shaft torque in the gearbox increase larger than approximately zero then the forces acting in the gear mesh will act in only one direction and the drive train will be aligned and tension will increase.
If the main shaft torque in the gearbox decrease below approximately zero then the forces acting in the gear mesh will act in only one direction, but now in an opposite direction and the drive train will be aligned and tension will increase.
In wind turbines it is known that the dynamic impacts induced by periodic load inversions, i.e. backlash fenomena, propagate through the drive train and can be amplified due to the excitations introduced by rotor and generator torque variations so that they may cause the failure of the wind turbine drive train.
Due to the variations of rotor and generator torques, the drive train is excited dynamically producing a permanently varying pretension. In certain states the pretension of the drive train is completely released or even inversed. The inversion of the pretension produces backlashes which can amplify due to the excitations introduced by the varying rotor and generator torque.
Another drawback of backlashes is that they are an important source of noise.
To the applicant knowledge it is not known prior art specifically addressed to overcome the difficulties with backlashes in wind turbines. There is indeed prior art teaching the use of generator torque control means and pitch control means for reducing the drive train loads in normal operational states and also prior art teaching the use of torque limiting devices in special wind situations such as in the event of gusts, but it is not known prior art focused in avoiding idling situations where the torque is random and shifting in direction with different unwanted potential consequences, including the production of noise.